This invention relates, in a magnetic disk having ultrathin carbon protective film 4 nm or less in thickness, to a relation between the protective film property and the lubricant film thickness which can markedly improve the wear resistance of the magnetic disk. Further, it relates, in a magnetic disk apparatus having a mechanism for feeding a lubricant into the apparatus, to a relation between the film property of the protective film of the magnetic disk, the lubricant supplied from the apparatus, and the lubricant film thickness which can impart a high reliability to the magnetic disk apparatus.
With recent trend toward higher recording density in magnetic disk apparatuses, the use of thinner protective film is growing in order to narrow the distance between the magnetic head and the magnetic film of the magnetic disk. For protective film of magnetic disks, there has hitherto been used amorphous carbon film or diamond-like carbon (DLC) film. With the tendency of recent years toward the use of thinner film, however, with the object of forming a DLC film more excellent in strength, such processes have been proposed as the chemical vapor deposition (CVD) method, ion beam deposition (IBD) method and filtered cathodic arc method.
In DLC film, there exist in the film carbon bonds of SP2 and SP3 structures and bonds of carbon with hydrogen. In particular, the physical property of DLC film varies greatly according to the amount of hydrogen in the film. It is known that, in general, the film hardness becomes maximum at a certain hydrogen amount and the hardness decreases when a more amount of hydrogen is incorporated thereinto because then hydrocarbon structures increase gradually. Accordingly, the optimization of hydrogen amount in DLC film is an important problem in controlling the film property. To deal with the problem, JP-A-6-195694 specifies the atomic ratio of carbon to hydrogen to be not less than 60/40 and not more than 90/10.
Further, JP-A-9-128732 discusses a correlation of film property with hydrogen amount by using the fluorescence intensity ratio of Raman spectrum and specifies the hydrogen amount at 10-37 at %. In these prior examples, since the thickness of protective film is very large, namely not less than 10 nm, the film property evaluation of protective film could be conducted in a simple and easy manner by using FT-IR (Fourier Transform Infrared Spectrometry), Raman spectrometry, etc.
In the prior techniques, however, the film property evaluation of ultrathin, as 5 nm or less, DLC protective film is difficult to attain, since the film thickness is too small, by such methods of determination as FT-IR or Raman described above because the detection signal becomes too weak. The present inventors have found that even when determination is made with a protective film of increased thickness to cope with the difficulty, an accurate evaluation of film property cannot be attained because the property of the film of increased thickness is not the same as that of a protective film of a thickness used in practice owing to difference in film-forming temperature and film-forming rate. Accordingly, it is intended by the present inventors to establish a proper evaluation method which can determine the film property of ultrathin DLC protective film and to provide a magnetic disk on the basis of the evaluation method.
Up to now, on the protective film of a magnetic disk is coated a fluorine-containing lubricant. The lubricant generally used is one called perfluoropolyether, and the film thickness is about 1-3 nm. However, nothing has hitherto been reported on a relation between protective film and lubricant film, particularly on a relation between the film property of thin protective film and the film thickness of lubricating film. In view of such situations, the present inventors have found an optimum range regarding the relations of these film thicknesses.
The prior technology for feeding a lubricant as a gas into a magnetic disk apparatus comprises providing a lubricant reserver in the head disk assembly. The object of supplying a lubricant is to decrease the spinning off of lubricant due to rotation and heat.
However, in the prior art, no due consideration has been given to the material and adsorption characteristic of a lubricant to be supplied, the material and adsorption characteristic of lubricant film formed on the magnetic disk, and the combination thereof, the combination of the film property of protective film with the material of lubricant to be supplied, and the combination with the film thickness of lubricant film after having been supplied. The present inventors have found that in the prior art methods, even when a lubricant is fed to a magnetic disk or head disk interface, the reliability cannot always be improved.
In the prior art method, further, fouling of the magnetic head cannot always be prevented depending on the lubricant used in supplying, which leads to lowering of reliability. The present inventors have further found that, since no adequate investigation has been made on the congeniality between the film property of thin protective film of a magnetic disk and the lubricant fed from the apparatus, the reliability of a magnetic disk apparatus cannot always be improved depending on the combination thereof.
Particularly, since DLC film generally shows a low adsorption energy of lubricant film unlike amorphous carbon film, due consideration must be given to the relation of lubricant film with protective film. Thus, a lubricant film on DLC film, which has a low adsorption energy, in some cases decreases greatly in its amount during the operation of the apparatus owing to spin-off (scattering of lubricant due to rotation of the magnetic disk) and pick-up by the magnetic head (a phenomenon wherein the lubricant is scratched off by the magnetic head and decreases its amount when the magnetic head and the magnetic disk contact with each other). In such cases, it is important to determine the optimum combination of the lubricant film thickness of the magnetic disk with the film property of protective film.
Presently, the thickness of protective film of magnetic disks is not more than 4-5 nm. In such an ultrathin film, it has become more difficult to secure wear resistance reliability for contact of a magnetic head with a magnetic disk, and it has become difficult to obtain a satisfactory result by optimizing the film property on the basis of hydrogen amount determined by the method of evaluation for DLC protective film as used in prior art techniques. Further, though the previous trend was to pursue high hardness films, in the case of ultrathin film, brittleness to deformation caused by underlayer material, etc., or elasticity to high speed, high friction force contact of a magnetic head with a magnetic disk becomes a problem. As a result, film is required which has both an appropriate hardness and an appropriate elasticity. On the other hand, with the trend toward the use of thin protective film, the contribution of lubricant film pertaining to wear resistance has increased, and importance has been attached to the optimization design of lubricant film suited to protective film.
In view of the above-mentioned problems, the object of this invention is to provide a magnetic disk which is excellent in durability even when the thickness of protective film is small, 4 nm or less, in more particular, to provide, for the purpose of improving the reliability of a magnetic disk apparatus, to provide the optimum combination of the film property of ultrathin protective film 4 nm or less in thickness, the material of lubricant film, and the thickness of lubricant film.
To solve the above-mentioned problems, according to this invention, there is provided a magnetic disk comprising a non-magnetic substrate and, provided thereon, at least a magnetic metal film, a carbon protective film and a fluorine-containing lubricant film, wherein the carbon protective film is a DLC film 4 nm or less in thickness, and the ratio of absorption intensity resulting from the Cxe2x80x94H bond near 2,920 cmxe2x88x921 determined by FT-IR using ATR to absorption intensity resulting from the Cxe2x80x94F bond of the lubricating film is 0.035-0.060.
As a result, a magnetic disk can be provided which has adequate hardness and elasticity, is covered with an adequate amount of lubricant film and is excellent in wear resistance reliability.
It is generally considered that the carbon protective film assumes an amorphous structure wherein SP3 bonds of diamond structure and SP2 bonds of graphite structure are present in admixture. By means of FT-IR measurement, the amount of hydrogen in the carbon protective film can be evaluated from the absorption spectra of lattice vibrations of the above-mentioned SP2- and SP3-bonded CH2, CH3, etc. However, since the carbon protective film of the magnetic disk aimed at in this invention is an ultrathin film 4 nm or less in thickness, a usual FT-IR reflection spectrum is insufficient in sensitivity. The present inventors have found that by using the ATR (Attenuated Total Reflectance) method, the surface sensitivity of FT-IR is improved and the evaluation of film property of carbon protective film becomes possible even for the above-mentioned ultrathin film.
The xe2x80x9cATR methodxe2x80x9d refers to a method which comprises contacting a sample to a prism having a high refractive index, entering infrared light thereinto, and observing a phenomenon wherein the evanescent wave developed at the interface between the prism and the sample at the time of infrared light incidence is absorbed to the sample, resultantly to cause change in the amount of light which passes through the prism.
The present inventors have further found that the ratio of absorption intensity resulting from the CH2 bond near 2920 cmxe2x88x921 to absorption intensity resulting from the CF bond of lubricant film is correlated with wear resistance and assumes a maximum value in a specific region (not less than 0.35 and not more than 0.060). It is considered that when the intensity is not more than 0.035, wear resistance deteriorates because the amount of hydrogen in carbon protective film is small and hence elasticity is low. On the other hand, when the intensity ratio is not less than 0.060, wear resistance lowers steeply. This is presumably because the amount of hydrogen in carbon protective film is too large, hence the density of protective film decreases and its hardness lowers. However, since the above-mentioned intensity ratio has been normalized by the absorption intensity of the CF bond of lubricant film, when the lubricant film thickness changes the optimum amount of hydrogen in protective film also changes. This invention gives a guide to wear resistance design not only of protective film but including lubricant film.
The above-mentioned magnetic disk can secure a sufficient durability even when the thickness of carbon protective film is not more than 4 nm. When the thickness of the carbon protective film is more than 4 nm, spacing loss develops in recording and regeneration at the magnetic head, which is unfavorable for a high density recording medium.
In another means of this invention, there is provided a magnetic disk apparatus which comprises a magnetic disk built-in within the apparatus and comprising a non-magnetic substrate and, provided thereon, at least a magnetic metal film and carbon protective film, wherein the carbon protective film is a diamond-like carbon (DLC) film having a film thickness of 4 nm or less, and a mechanism for supplying into the apparatus a lubricant represented by the chemical formula (1) as a gas, wherein, after preparation of the magnetic disk apparatus, the magnetic disk built-in within the apparatus is measured by FT-IR using ATR and the film property of the protective film is controlled such that the ratio of infrared absorption intensity resulting from the Cxe2x80x94H bond near 2920 cmxe2x88x921 to infrared absorption intensity resulting from the Cxe2x80x94F bond of lubricant film may be 0.035-0.060.
HOCH2CF2(OC2F2)p(OCF2)qOCF2CH2OH xe2x80x83xe2x80x83(1) 
wherein p is 0 or an integer of 1 or more, q is 0 or an integer of 1 or more, and the average molecular weight of the lubricant is 600-2400.
In the case of a magnetic disk apparatus having a mechanism for supplying a lubricant of formula (1) into the apparatus, after preparation of the apparatus, that is, after completion of assembling and inspection of the apparatus, the lubricant gas supplied into the apparatus has been adsorbed to the magnetic disk, and the lubricant film has a thickness of about 1.5 nm-2.5 nm. At this time the film property of the protective film is controlled such that the ratio of infrared absorption intensity resulting from the Cxe2x80x94H bond near 2920 cmxe2x88x921 to infrared absorption intensity resulting from the Cxe2x80x94F bond of lubricant film obtained by the above-mentioned measurement may be 0.035-0.060, whereby a magnetic disk apparatus with a high reliability can be provided.
Other objects, features and advantages of the invention will become apparent from the following description of the embodiments of the invention taken in conjunction with the accompanying drawings.